In general, in order to improve work efficiency and working range, construction machinery such as excavators have an upper swing body installed to be capable of swinging on a lower moving body. The upper swing body is stopped by means of a swing brake apparatus, so that the operator may control the swinging of the upper swing body. An example of such a swing brake apparatus is illustrated in FIG. 1.
In a swing system of a hydraulic excavator, power is transferred through a swing hydraulic motor and a swing speed reducer to a swing bearing mounted on a main frame. The shaft of the swing hydraulic motor is connected to a sun gear of the swing speed reducer through a spline, and when the shaft of the swing motor does not rotate, the swing speed reducer and the swing bearing also do not rotate, thus stopping the swing system.
According to the work characteristics of an excavator, the occurrence of undesired swinging can lead not only to lower efficiency and damage to equipment, but also to the loss of life. A representative example is the occasional occurrence of undesired swinging when a vehicle is positioned or working on a slope while the engine is stopped or idling.
Further, equipment damage and loss of life can be caused by a clash between the driving of a swing motor and the stopping of a brake when a swing brake operates while an operator is performing or begins to implement a swinging operation. Therefore, a swing brake system needs to be designed at least so that the system is deployed when an operator is performing a swinging operation.
Referring to FIGS. 1 and 2, to describe the operating principle of a swing brake, the shaft of a swing motor is connected to a plurality of disks, the disks have a structure in which a plurality of brake plates fixes the disks to prevent movement thereof, and the brake plates are pressed firmly against the disks by means of a tensile member such as a brake return spring, so that the swing brake is normally always applied.
The brake plates are pressed firmly by a strong force, but have a structure in which the brake plates may be separated from the disks by means of a hydraulic apparatus such as a brake piston.
Accordingly, as illustrated in FIG. 1, in a swing brake 20, when hydraulic pressure is applied to a swing brake valve 30 through a passage, a brake piston presses a brake return spring in a reverse direction by means of the applied hydraulic pressure, whereupon a disk connected to a shaft of a hydraulic motor is separated from a plate assembled to a housing, so as to disengage the swing brake 20.
In the case of such a related art hydraulic excavator, when the swing motor that is configured as a hydraulic motor receives power through a hydraulic line, hydraulic pressure supplied to a hydraulic line for swing driving or a pilot hydraulic line for swing actuation may be used to directly drive the hydraulic brake valve and disengage the swing brake.
However, in the case of hybrid excavators, because the hydraulic swing motor has been changed to an electric swing motor so as to omit the hydraulic line from the swing system, a hydraulic signal according to the movement of a swing joystick cannot actuate the electric swing motor. Unlike a hydraulic swing motor, when using the electric swing motor, a swing signal is generated in a control unit, whereupon the swing motor immediately responds and is driven. Thus, there arise the problems of damage and accidents due to a clash between the operations of the swing motor and the swing brake, when the swing motor is operated before or during the disengaging of the swing brake.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.